β-Diketiminate zinc Complexes for the hydroamination of alkynes

Article abstract of DOI:10.1002/ejic.200900998

A series of electronically and sterically modified ss-diketiminate methylzinc complexes [{N,N′-bis(2,6-diisopropylphenyl)-β- diketiminato}methylzinc] (1), [{N,N′-bis(2-isopropylphenyl)-β- diketim.mato}melhylzinc] (2), [{N,N′-bis(2,4,6-trimethylphenyl)-β-

Full text of DOI:10.1002/ejic.200900998

FULL PAPER
DOI: 10.1002/ejic.200900998
β-Diketiminate Zinc Complexes for the Hydroamination of Alkynes
Mustafa Biyikal,[a] Karolin Löhnwitz,[b] Nils Meyer,[c] Maximilian Dochnahl,[a][‡]
Peter W. Roesky,*[b] and Siegfried Blechert*[a]
Keywords: Alkynes / Cyclization / β-Diketiminates / Hydroamination / Zinc
A series of electronically and sterically modified β-diketimin-
ate methylzinc complexes [{N,NЈ-bis(2,6-diisopropylphenyl)-
ation of nonactivated alkynes and show high catalytic ac-
tivity in the presence of the cocatalyst [PhNMe2H][SO3CF3].
The zinc complex 1 shows the highest catalytic activity
in most of the cyclization reactions. In this context, it was
possible to isolate the intermediate, which was formed by
β-diketiminato}methylzinc]
(1),
[{N,NЈ-bis(2-isopropyl-
phenyl)-β-diketiminato}methylzinc] (2), [{N,NЈ-bis(2,4,6-tri-
methylphenyl)-β-diketiminato}methylzinc] (3), [{N,NЈ-bis(4-
methoxyphenyl)-β-diketiminato}methylzinc] (4), a bis(β-di-
ketiminato)zinc compound [bis{N,NЈ-bis(4-methoxyphenyl)-
β-diketiminato}zinc] (5), and a β-diketiminate bis(trimethyl-
silylamido)zinc complex [{2-(1-cyclohexylimidazolidine-2-
the reaction of the precatalyst
1 and the cocatalyst
[PhNMe2H][SO3CF3]. The resulting zinc catalyst [{N,NЈ-
bis(2,6-diisopropylphenyl)-β-diketiminato}(trifluoromethane-
sulfonate)zinc]·thf (7) was structurally characterized by sin-
ylidene)-1-methylethylidene-(2,6-diisopropylphenyl)aminato}- gle-crystal X-ray diffraction. The zinc complex 7 show the
bis(trimethysilylamido)zinc] (6) were prepared and structur-
ally characterized by single-crystal X-ray diffraction. All
methylzinc compounds exhibit a trigonal-planar coordinated
zinc atom, with the exception of polymeric compound 4, in
which intermolecular coordination of the OMe group to the
zinc atom additionally takes place. All zinc complexes were
investigated as catalysts in the intramolecular hydroamin-
same catalytic activity in the hydroamination when an equi-
molar mixture of the precatalyst 1 and the cocatalyst was
used. It is supposed that the high steric bulk of the precata-
lyst 1 protects the Lewis acid zinc center from polar func-
tional groups but allows interactions for the cyclization pro-
cess.
which makes their routine preparation and application in
synthesis problematic. Unlike the early transition metals,
the late transition metals have a much higher tolerance
towards water, oxygen impurities, and functional groups.
Therefore, they have a broader potential for application in
organic synthesis. Most of these catalysts are based on rela-
tively expensive gold, palladium, platinum, or on nickel.
Moreover, for nonactivated substrates, most of the late-
transition-metal catalysts show limited scope, modest selec-
tivity, and sluggish reaction rates.
Organozinc complexes are extensively used in organic
syntheses.[14] We developed aminotroponiminate methylzinc
complexes as catalysts for intramolecular hydroamina-
tion.[15–17] In this context, we investigated the influence of
steric modifications of the alkyl groups at the nitrogen
atoms of the aminotroponimine ligand and of electronic
modifications by using aminotroponiminates having a
phenylsulfanyl in 5-position of the ligand. We were able to
show the major influence of the steric and electronic envi-
ronment around the zinc atom on both the reactivity and
stability of the corresponding complexes.[17] The resulting
zinc complexes possess interesting advantages relative to
other metal catalysts such as (i) they show a very high toler-
ance towards polar functional groups and (ii) they are re-
markably stable towards air and moisture. So far, we fo-
cused on aminotroponiminate zinc complexes. Herein, we
Introduction
The catalytic addition of organic amine N–H bonds to
multiple C–C bonds is a powerful and atom-economical
method for the synthesis of nitrogen-containing molecules.
Hydroamination has been studied extensively with various
metal catalysts. The widespread search for homogeneous
catalysts for this process has begat a burgeoning and mech-
anistically diverse area of research that has utilised lith-
ium,[1] group 4 metals,[2] the lanthanides,[3–6] the platinum
metals,[7] the alkaline earth metals,[8] copper,[9] silver,[10] and
gold.[11] The scope of catalytic hydroamination reactions
has been reviewed recently.[12,13] The lanthanides are espe-
cially highly efficient catalysts for the hydroamination of
various multiple bonds, but they display limited functional
group tolerance and high air- and moisture sensitivity,
[a] Institut für Chemie, Technische Universität Berlin,
Strasse des 17. Juni 115, 10623 Berlin, Germany
Fax: +49-30-3142-3619
E-mail: blechert@chem.tu-berlin.de
[b] Institut für Anorganische Chemie, Karlsruher Institut für Tech-
nologie (KIT),
Engesserstr.15, 76128 Karlsruhe, Germany
Fax: +49-721-608-4854
E-mail: roesky@kit.edu
[c] Institut für Chemie und Biochemie, Freie Universität Berlin,
Fabeckstrasse 34-36, 14195 Berlin, Germany
[‡] Present address: BASF SE, Global Research Crop Protection,
67056 Ludwigshafen, Germany
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β-Diketiminate Zinc Complexes for the Hydroamination of Alkynes
report on β-diketiminate (BDI) zinc complexes as catalysts pared in one step by refluxing 2,4-pentadione with two
for intramolecular hydroamination. Even though β-diket- equivalents of the corresponding aniline. The introduction
iminate complexes of cobalt, nickel, copper and zinc are of substituents at the N-aryl ring leads to altered catalytic
known since the late 1960s,[18–20] the first catalytic applica- properties of the β-diketiminate zinc complexes.
tions were reported as late as the 1990s.[21–26] Coates et al.
As a result of the successful application of β-diketimine
have demonstrated that zinc alkoxides with bulky β-diket- ligands, we decided to develop a novel type of a β-diket-
iminate ligands in the coordination sphere show very high imine ligand 10 starting from malononitrile (Scheme 1). To
rates for the (living) copolymerization of cyclohexene oxide the best of our knowledge, so far this type has not been
and CO2 to make polycarbonates,[27–30] the synthesis of po- used in organometallic complexes. In principle, it should
ly(lactic acid) by stereoselective ROP of lactide,[31,32] and also be possible to synthesize chiral versions. Appropriate
the ring-opening polymerization of β-butyrolactone and γ- imine oxazoline ligands generated from chiral 1,2-amino
valerolactone.[33] Rieger et al. have shown that the ethylsulf- alcohols, their corresponding zinc complexes, and their ap-
inate ligand is a highly efficient initiating group for the β- plication in catalyzed copolymerization reactions of CO2
diketiminate-zinc-catalyzed copolymerization reaction of and epoxides are known.[37]
CO2 and epoxides.[34,35]
Herein we report the synthesis of six β-diketiminate zinc
complexes (compounds 2–7; Figure 1, Schemes 3 and 4) in-
cluding the novel type of an imidazoline version 6 and their
application as catalysts for the hydroamination of nonacti-
vated alkynes.
Scheme 1. Synthesis of the ligand 10. Reagents and conditions: (a)
(CH3)3SiCl, ethanol, diethylether, room temperautre, 1 h; (b) N-
cyclohexylethane-1,2-diamine, room temperature, overnight, 37%;
(c) MeLi, 0 °C, 1.5 h, 51%; (d) 2,6-diisopropylaniline, conc. HCl,
ethanol, 95 °C, 4 d, 30%; (e) Amberlite® IRA-400(OH), methanol,
room temperature, overnight, 81%.
For the synthesis of the ligand 10, malononitrile was con-
verted in one step with (CH3)3SiCl and two equivalents of
ethanol to generate in situ ethyl 2-cyano-acetimidate hydro-
chloride.[38] After 1 h at room temperature, N-cyclohexyl-
ethane-1,2-diamine[39] was added, and nitrile 8 was isolated
in 37% yield. Subsequent conversion of 8 with methyllith-
ium delivered the ketone 9 in a moderate yield of 51%. The
ketone 9 was then condensed with 2,6-diisopropylaniline by
heating in ethanol in the presence of HCl for 4 d at 95 °C.
Ligand 10 was obtained as the hydrochloride salt by simple
filtration in 30% yield. Afterwards, the free ligand 10 was
easily obtained by removing the hydrochloride using Am-
Figure 1. Structure of the β-diketiminate zinc complexes 1–5.
berlite® IRA-(400)(OH) with a high yield of 81%.
Metal Complex Synthesis
Results and Discussion
The methylzinc complex 1 has been described and was
Ligand Synthesis
prepared by reaction of dimethylzinc with the N,NЈ-bis(2,6-
Several synthetic routes to β-diketimine ligands have diisopropylphenyl)-β-diketimine.[40] The same method was
been reported.[28,36] The ligands of complexes 1–5 were pre- used for the synthesis of compounds 2–5. Complex 4 was
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available as a mixture with 5 (9:1), but could be obtained
Single crystals of all the new compounds could be ob-
in pure form by crystallization. To investigate the catalytic tained and the solid-state structures were established by sin-
activity of side product 5, we used half an equivalent in- gle-crystal X-ray diffraction. Only the data collected from
stead of one equivalent of dimethylzinc to yield 5 exclu- 2 were poor and prohibited a full refinement. However, the
sively (Scheme 2).
connectivity of 2 and its composition were deduced. Com-
pound 3 crystallizes in the monoclinic space group P21/n
and has two molecules in the asymmetric unit. As observed
earlier for compound 1, the zinc atom in compound 3 is
coordinated by two nitrogen atoms and one carbon atom,
which results in a planar, triangular arrangement (Fig-
ure 2). Both Zn–N bond lengths are equal within error [e.g.
Zn1–N1 1.963(3) Å and Zn1–N2 1.954(3) Å]. The metalla-
cyclohexane ring formed by the β-diketiminate ligand and
the zinc atom is almost planar, which indicates a delocaliza-
tion of the π electrons. The Zn–C bond length is in the
expected range, Zn1–C6 1.943(4) Å and Zn2–C30
1.940(4) Å. The structure consists of individual molecules,
and there are no intermolecular contacts. This is in contrast
to the solid-state structure of compound 4 (Figure 3). Com-
pound 4, which crystallizes in the monoclinic space group
P21/n with four molecules in the unit cell, forms a polymer
in the solid state (Figure 3 bottom). The polymer is formed
by intermolecular coordination of one OMe group to a zinc
atom of an adjacent molecule. The Zn–O1Ј bond distance
is 2.368(2) Å. In contrast to compounds 2 and 3, the Zn
atom is thus four coordinate. The O1Ј atom is attached al-
most perpendicularly to the N1–Zn–N2 plane, and the N1–
Zn–O1Ј and N2–Zn–O1Ј bond angles are 97.31(6) and
96.00(7)°, respectively. The methyl group is slightly bent out
of plane, which results in a C20–Zn–O1Ј angle of 99.43(9)°.
The Zn–N and Zn–C bond distances are not altered relative
to compound 3 [Zn–N1 1.978(2) Å, Zn–N2 1.980(2) Å, and
Zn–C20 1.962(2) Å]. The bis(β-diketiminate) complex 5
crystallizes in the monoclinic space group P21/c with four
molecules in the unit cell (Figure 4). The zinc atom is four
coordinate with two ligands and forms a distorted tetrahe-
dral environment. The N–Zn–N angles inside the metalla-
cyclohexane ring formed by the β-diketiminato ligand and
the zinc atom are N1–Zn–N2 97.78(7) and 97.42(8)°. The
other N–Zn–N angles vary from 112.75(8) to 118.40(8)°.
Scheme 2.
These observations are consistent with our earlier obser-
vations with ether-functionalized aminotroponimines,
which give the corresponding bis(aminotroponiminate) zinc
compounds.[17b]
For the preparation of the first hybrid imine imidazoline
complex 6, ligand 10 was treated with bis(trimethylsilyl)-
amide zinc at room temperature and 6 was isolated in a
yield of 73% (Scheme 3).
Scheme 3.
All complexes have been characterized by standard ana-
lytical/spectroscopic techniques, and the molecular struc-
tures were confirmed by single-crystal X-ray diffraction in
the solid state. A comparison of the 1H and 13C{1H} NMR
spectra of the starting material ZnMe2 (1H δ = 0.51 ppm,
13C{1H} δ = –4.2 ppm)[41] with the methyl complexes 2 (1H
δ = –0.58 ppm, 13C{1H} δ = –17.9 ppm), 3 (1H δ =
–0.56 ppm, 13C{1H} δ = –18.7 ppm), and 4 (1H δ =
–0.40 ppm, 13C{1H} δ = –20.8 ppm) shows that the 1H
NMR and the 13C{1H} NMR signal of the Zn–CH3 group
shifts to a higher field for all complexes. The observed
NMR signals of the β-diketimine zinc complexes are as ex-
pected. In the NMR spectra of compound 2, two isomers
are observed. We interpret the two sets of signals in terms
of hindered rotation of the 2-iPrC6H4 group around the C–
N axis.
Figure 2. Perspective ORTEP view of the molecular structure of 3.
Shown is one of two crystallographic independent molecules. Ther-
mal ellipsoids are drawn to encompass 50% probability. Hydrogen
atoms are omitted for clarity. Selected bond lengths [Å] and angles
[°]: Zn1–N1 1.963(3), Zn1–N2 1.954(3), Zn1–C6 1.943(4), Zn2–N3
1.967(3), Zn2–N4 1.940(3), Zn2–C30 1.940(4); N1–Zn1–C6
128.6(2), N1–Zn1–N2 96.09(13), N2–Zn1–C6 135.2(2), N4–Zn2–
C30 134.8(2), N3–Zn2–N4 96.49(14), N3–Zn2–C30 128.7(2).
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β-Diketiminate Zinc Complexes for the Hydroamination of Alkynes
The Zn–N bond distances are in the expected range of unit cell (Figure 5). The zinc atom is surrounded by three
1.975(2) Å and 2.001(2) Å. Compound 6 crystallizes in the nitrogen atoms, which results in a planar triangular ar-
monoclinic space group P21/n with four molecules in the rangement The Zn–N bonding distances of the asymmetric
β-diketiminato ligand are in a similar range [Zn–N1
1.944(2) Å and Zn–N2 1.938(2) Å]. In contrast, the Zn–N
bond of the bis(trimethylsilylamido) group is significantly
shorter [Zn–N4 1.897(2) Å], which is a result of the stronger
electrostatic interaction.
Figure 5. Perspective ORTEP view of the molecular structure of 6.
Thermal ellipsoids are drawn to encompass 50% probability. Hy-
drogen atoms are omitted for clarity. Selected bond lengths [Å] and
angles [°]: Zn–N1 1.944(2), Zn–N2 1.938(2), Zn–N4 1.897(2), N4–
Si1 1.708(2), N4–Si2 1.708(2); N1–Zn–N2 97.52(7), N1–Zn–N4
138.65(8), N2–Zn–N4 123.48(8).
Hydroamination/Cyclization Catalysis
Figure 3. Perspective ORTEP view of the molecular structure of 4.
Encouraged by the results achieved with the hydroamin-
Top: thermal ellipsoids are drawn to encompass 50% probability.
ation with the aminotroponiminate methyl complexes,[15–17]
Bottom: perspective cut out of the polymeric solid-state structure
of 4 showing the atom labelling scheme. Hydrogen atoms are omit-
ted for clarity. Selected bond lengths [Å] and angles [°]: Zn–N1
1.978(2), Zn–N2 1.980(2), Zn–C20 1.962(2), Zn–O1Ј 2.368(2); N1–
Zn–N2 96.07(7), N1–Zn–C20 127.17(10), N2–Zn–C20 131.04(9),
N1–Zn–O1Ј 97.31(6), N2–Zn–O1Ј 96.00(7), C20–Zn–O1Ј 99.43(9).
we applied complexes 1–6 as precatalysts in the intramolecu-
lar hydroamination of nonactivated alkynes (Table 1). Com-
plexes 1–6 show high catalytic activity in the presence of the
cocatalyst [PhNMe2H][SO3CF3] prepared in our group. To
compare the catalytic activity of complexes 1–6, initial ex-
periments were focused on the intramolecular hydroamin-
ation of the challenging substrates 11a–g. The first catalyst
screening experiments were carried out with substrates 11a–
d, and it was shown that amines with bulky substituents in
the position α to the amine displays a significantly decreased
reaction rate (Table 1, Entries 3, 4). In all cases, the genera-
tion of the cyclic products 12a–d was monitored by 1H NMR
spectroscopy. In the cyclization reaction of the α-unsubsti-
tuted substrate 11a, the highest catalytic activity is observed
with precatalyst 1, which required 20 h to reach a 93% con-
version (Table 1, Entry 1). The more polar p-methoxybenzyl-
protected substrate 11b shows an even higher reaction rate
(Ͼ99% within 23 h) with precatalyst 2 (Table 1, Entry 2). In
comparison to 11a, the α-ethylated substrate 11c was con-
verted with precatalysts 1 and 6 after longer reaction times
(Table 1, Entry 3). The cyclization reaction of the α-iso-
propylated substrate 11d with precatalyst 2 took only 90 h
for a conversion of 98% (Table 1, Entry 4).
Figure 4. Perspective ORTEP view of the molecular structure of 5.
One of two crystallographic independent molecules is shown. Ther-
mal ellipsoids are drawn to encompass 50% probability. Hydrogen
atoms are omitted for clarity. Selected bond lengths [Å] and angles
[°]: Zn–N1 1.990(2), Zn–N2 1.977(2), Zn–N3 1.975(2), Zn–N4
2.001(2); N1–Zn–N2 97.78(7), N1–Zn–N3 118.40(8), N1–Zn–N4
113.21(8), N2–Zn–N3 118.21(8), N2–Zn–N4 112.75(8), N3–Zn–N4
97.42(8).
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Table 1. Hydroamination of the aminoalkynes 11a–g catalyzed by the precatalysts 1–6.[a]
[a] Reagents and Conditions: Substrates 11a–d (0.74 mmol), precatalyst (1 mol-%), [PhNMe2H][SO3CF3] (1 mol-%). Substrates 11e–g
(0.36 mmol), precatalyst (10 mol-%), [PhNMe2H][SO3CF3] (10 mol-%), C6D6, 60 °C. Conversions are determined by 1H NMR spec-
troscopy. [b] Isolated yield after hydrolysis. [c] The reaction was performed at room temperature.
To obtain more polar substrates for the hydroamination, pared (Table 1, Entries 5–7). At first, the substrate 11e was
electronically modified N-aryl substrates 11e–g were pre- introduced in cyclization reactions, and the product 12e was
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β-Diketiminate Zinc Complexes for the Hydroamination of Alkynes
1
observed by H NMR spectroscopy after 1 h with precata-
lyst 1 in excellent conversion rates (Table 1, Entry 5). In
the hydroamination of 11f, precatalyst 1 showed the highest
catalytic activity, and the ketone 12f was isolated as product
after hydrolysis of the reaction mixture in a moderate yield
of 76% (Table 1, Entry 6). In comparison to substrate 11e,
substrate 11f showed clearly lower reaction rates, which we
assign to the presence of the pyrimidyl nitrogen atoms; they
decrease the catalytic activity of the zinc complexes through
coordination. To prove this assumption, we introduced sub-
strate 11g with a less nucleophilic amine group in the hy-
droamination reactions and observed high conversion rates
and high yields of the ketone 12g even at room temperature.
The best results were obtained with precatalyst 1. Accord-
ing to these results, zinc complexes with sterically less-
demanding ligands show lower catalytic activity than we
have observed, particularly in the case of the zinc complexes
4 and 5 (Table 1, Entries 1–7).
Scheme 4.
with four molecules in the unit cell (Figure 6). In contrast
to compounds 1–6, an additional equivalent of thf is coor-
dinated to the zinc atom in the solid state, which results in
a four-coordinate zinc atom. The zinc atom is thus in the
center of a distorted tetrahedral coordination polyhedron.
Mechanistic Insight
Since it is known that protons may catalyze the hydroa-
mination reaction,[42] we treated substrate 11a with a cata-
lytic amount of the cocatalyst [PhNMe2H][SO3CF3] in the
absence of any zinc compound at 120 °C (Table 2, Entry 1).
No reaction was observed under these conditions. In con-
trast, a tremendous acceleration of the reaction was mea-
sured with complex 1 as precatalyst upon addition of the
cocatalyst [PhNMe2H][SO3CF3] for all reactions shown in
Table 1. Substrate 11d is converted in 90 h at 60 °C with a
precatalyst and cocatalyst loading of 1 mol-%. In compari-
son, 1 (catalyst loading: 10 mol-%) needs 20 d at 120 °C to
reach 70% conversion in the absence of the cocatalyst
(Table 2, Entry 2). It was speculated that the cocatalyst re-
moves the methyl group from the zinc complex in a proton-
ation step. To prove this assumption, an equimolar mixture
of precatalyst 1 and the cocatalyst [PhNMe2H][SO3CF3]
were treated to give [{N,NЈ-bis(2,6-diisopropylphenyl)-β-
diketiminato}(trifluoromethanesulfonate)zinc]·thf (7) with
a yield of 47% (Scheme 4).
Figure 6. Perspective ORTEP view of the molecular structure of 7.
Thermal ellipsoids are drawn to encompass 50% probability. Hy-
drogen atoms are omitted for clarity. Selected bond lengths [Å] and
angles [°]: Zn–N1 1.854(2), Zn–N2 1.936(2), Zn–O1 2.133(2), Zn–
O2 1.950(3); N1–Zn–N2 100.05(10), N1–Zn–O1 103.36(9), N1–
Zn–O2 116.36(11), N2–Zn–O1 112.37(9), N2–Zn–O2 119.82(13),
O1–Zn–O2 104.02(12).
Compound 7 was also tested as a catalyst in hydroamin-
ation reactions. Compound 7 converts substrate 11b in 93%
yield with a catalyst loading of 1 mol-% and shows the same
catalytic activity as the corresponding zinc catalyst gener-
ated in situ (Table 2, Entry 3).
In the hydroamination of alkynes, Zn(OTf)2 was also
used as a catalyst.[43] To exclude the assumption that
Zn(OTf)2 is generated in the reaction mixture by twofold
protonation of the zinc complexes and in order to catalyze
the hydroamination reaction, we tested Zn(OTf)2 (catalyst
loading: 1 mol-%) as catalyst to convert substrate 11c under
the same conditions described above. Interestingly, Zn-
(OTf)2 only shows very low catalytic activity for hydroamin-
ation, whereas a 78% conversion is observed for substrate
11c in 5 d (Table 2, Entry 4). In the case of complex 1 (pre-
catalyst loading: 1 mol-%) with a cocatalyst loading of
1.0 mol-%, the reaction results in 93% conversion in 40 h
(Table 1, Entry 3).
Table 2. Hydroamination of the aminoalkynes under various condi-
tions.
Entry Catalyst Catalyst
Cocatalyst
T
Substrate Time Conv.
loading [%] loading [%] [°C]
[h]
[h]
1
2
–
1
1
1
7
1
–
10
1
1
1
10
–
1
1
–
120
120
60
60
60
11a
11d
11d
11b
11b
11c
11c
90
480
90
30
30
0
73
93
96[a]
93[a]
93
3
4
1
1
1
–
60
60
40
120
Zn(OTf)2
78
[a] Yield is referred to the introduced reference compound hexa-
methylbenzene.
Conclusions
Complex 7 was characterized by standard analytical
techniques, and the molecular structures were confirmed by
This work demonstrates that all the investigated com-
single-crystal X-ray diffraction in the solid state. Com- plexes 1–6 are effective catalysts in hydroamination of non-
pound 7 crystallizes in the monoclinic space group P21/n activated alkynes with the addition of cocatalyst
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P. W. Roesky, S. Blechert et al.
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60 °C for the stated duration of time. The hydroamination products
were purified by flash column chromatography on silica gel.
[PhNMe2H][SO3CF3]. Subtle modifications of the ligands
show dramatic effects on the catalytic activity of the com-
plexes 1–6. Thus, we suggest that accessibility to the reac-
tive metal center is an important factor in β-diketiminate
zinc complex design. However, the catalytic activities of the
β-diketiminate zinc complexes 1–6 strongly depend on the
ligand architecture and on the properties of the employed
substrates. Especially, zinc complex 1 showed the highest
catalytic activity in most of the cyclization reactions. It is
proposed that the high steric bulk of precatalyst 1 protects
the Lewis acid zinc center from high polar functional
groups but allows interactions for the cyclization process.
In this context, it was possible to isolate the intermediate,
Ligand Synthesis
(1-Cyclohexyl-imidazolidine-2-ylidene)acetonitrile (8): To a solution
of malononitrile (255 mg, 3.86 mmol) and ethanol (415 mg,
9.01 mmol) in diethyl ether (4 mL) was added (CH3)3SiCl (424 mg,
3.90 mmol). After 1 h at room temperature N-cyclohexylethane-
1,2-diamine (538 mg, 3.78 mmol) was added, and the suspension
was stirred overnight. After the addition of concentrated NaHCO3
solution, the mixture was extracted with diethyl ether (2ϫ100 mL)
and dried with MgSO4. The solvent was removed under reduced
pressure and the residue was purified by flash column chromatog-
raphy (SiO2, cyclohexane/EtOAc, 1:3) to afford 8 as a white solid.
1
which was formed by reaction of precatalyst 1 and cocata- Yield: 271 mg (37%). M.p. 164 °C. H NMR (400 MHz, CDCl3):
δ = 1.12 (m, 1 H, CH2), 1.33 (m, 4 H, CH2), 1.70 (m, 1 H, CH2),
1.85 (m, 4 H, CH2), 3.05 (s, 1 H, CH), 3.09 (m, 1 H, CH), 3.45 (m,
4 H, CH2), 4.67 (br. s, 1 H, NH) ppm. 13C NMR (125 MHz,
CDCl3): δ = 25.4 (CH2), 25.5 (CH2), 29.6 (CH2), 35.4 (CH), 41.9
(CH2), 44.0 (CH2), 53.9 (CH), 124.2 (C), 163.8 (C) ppm. IR (ATR):
lyst [PhNMe2H][SO3CF3]. The resulting zinc catalyst 7
showed the same catalytic activity in hydroamination reac-
tions as did the precatalyst 1. The novel imidazoline zinc
complex 6 also showed high catalytic activity in hydroamin-
ation reactions. But unlike the β-diketimine complexes 1–5,
the advantage of the imidazoline zinc complex system is
that the synthetic route to this new type of ligands allows
the introduction of chiral centers such as chiral 1,2-di-
amines for catalyzed asymmetric synthesis. Further studies
are under current investigations.
ν = 3299, 2934, 2856, 2168, 1586, 1503, 1279, 1076, 968 cm–1. MS
˜
(EI, 70 eV, room temperature): m/z (%) = 191 (42) [M+], 148 (40),
109 (100), 80 (61), 69 (25), 55 (35), 45 (48), 41 (69). HRMS: calcd.
for C11H17N3 191.1423; found 191.1415.
1-(1-Cyclohexyl-imidazolidine-2-ylidene)propan-2-one (9): Com-
pound 8 (778 mg, 4.06 mmol) in thf (9 mL) was added dropwise to
a
solution of methyllithium (1.6  in diethylether, 13 mL,
20.80 mmol) at –10 °C, and the solution was stirred for 1.5 h at
0 °C. After the addition of HCl [1 ] at –30 °C, the mixture was
extracted with diethyl ether (2ϫ60 mL) and dried with MgSO4.
The solvent was concentrated under reduced pressure, and the resi-
due was recrystallized at –20 °C to obtain 9 as white crystals. Yield:
435 mg (51%). M.p. 120 °C. 1H NMR (400 MHz, CDCl3): δ = 1.11
(m, 1 H, CH2), 1.35 (m, 4 H, CH2), 1.70 (m, 1 H, CH2), 1.81 (m,
4 H, CH2), 2.00 (s, 3 H, CH3), 3.31 (m, 1 H, CH), 3.39 (m, 2 H,
CH2), 3.55 (m, 2 H, CH2), 4.61 (s, 1 H, CH), 9.37 (br. s, 1 H, NH)
ppm. 13C NMR (125 MHz, CDCl3): δ = 25.5 (CH2), 25.6 (CH2),
28.8 (CH3), 30.0 (CH2), 42.0 (CH2), 42.6 (CH2), 53.2 (CH), 75.6
Experimental Section
General Methods and Instruments: All reactions with air- or water-
sensitive compounds were carried out under dry nitrogen with stan-
dard Schlenk vacuum-line techniques. All NMR-tube scale reac-
tions were prepared in an N2-filled glove box. NMR spectra were
recorded on a Bruker AC 400 (1H, 400 MHz; 13C, 100 MHz) and
DRX 500 (1H, 500 MHz; 13C, 125 MHz) spectrometer and refer-
enced versus residual solvent shifts. The ratio between the substrate
and the product was calculated exactly by comparison of the inte-
gration of the corresponding signals. All products were analyzed
by 1H, 13C, 13C-DEPT, COSY, and HMQC NMR spectroscopy
and by IR spectroscopy, MS, HRMS and EA where possible. Infra-
red spectra were recorded on a Perkin–Elmer spectrometer 881 as
ATR (Attenuated Total Reflectance). MS and HRMS analyses
were carried out with a Finnigan MAT 95 SQ or a Varian MAT
711 spectrometer. Elemental analyses were carried out with a Vario
EL III instrument. Melting points were determined in sealed glass
capillaries under N2 with BÜCHI 535. The substrates 11b–d and
their cyclic hydroamination products 12b–d were previously de-
scribed in our group.[15] Prior to use, all substrates were purified
by bulb-to-bulb distillation or by flash column chromatography
over silica gel (40-63 µm). Toluene, thf, and diethyl ether were dis-
tilled under nitrogen from sodium, hexane was distilled under ni-
trogen from calcium hydride, and C6D6 was stored over K/Na alloy
before use. Dimethylzinc and the starting materials for the prepara-
tion of the substrates 11a–g were purchased from Acros Organics,
Aldrich and Fluka.
(CH), 162.8 (C), 191.0 (C) ppm. IR (ATR): ν = 3262, 2931, 2861,
˜
1594, 1542, 1512, 1281, 1223, 1071, 960, 716, 676 cm–1. MS (EI,
70 eV, room temperature): m/z (%) = 208 (56) [M+], 193 (9), 153
(18), 84 (100), 43 (52). HRMS: calcd. for C12H20N2O 208.1576;
found 208.1578.
[2-(1-Cyclohexyl-imidazolidine-2-ylidene)-1-methylethylidene]-(2,6-
diisopropylphenyl)amino Hydrochloride (10·HCl): A solution of 9
(867 mg, 4.16 mmol) and 2,6-diisopropylaniline (870 mg,
4.91 mmol) in ethanol (15 mL) and concentrated HCl (0.7 mL)
were heated for 4 d at 95 °C. Chloroform (7 mL) and ether (30 mL)
were then added to the solvent. After 24 h at –20 °C, the suspension
was filtered and 10·HCl was obtained as a white powder. Yield:
500 mg (30%). M.p. Ͼ230 °C. 1H NMR (400 MHz, [D6]DMSO):
δ = 0.92 (m, 3 H, CH2), 1.13 (d, J = 6.8 Hz, 12 H, CH3), 1.39 (m,
5 H, CH2), 1.63 (m, 2 H, CH2), 2.47 (s, 3 H, CH3), 2.82 (tt, J =
3.8, J = 11.5 Hz, 1 H, CH), 2.90 (septet, J = 6.8 Hz, 2 H, CH),
3.59 (br. s, 4 H, CH2), 3.87 (s, 1 H, CH), 7.28 (m, 2 H, CHAr), 7.38
(m, 1 H, CHAr), 8.29 (br. s, 1 H, NH), 9.44 (br. s, 1 H, HCl) ppm.
13C NMR (125 MHz, [D6]DMSO): δ = 19.4 (CH3), 23.1 (CH3),
24.4 (CH3), 24.5 (CH2), 25.0 (CH2), 28.0 (CH), 29.4 (CH2), 41.8
(CH2), 43.5 (CH2), 54.4 (CH), 74.5 (CH), 123.9 (CHAr), 128.9
Hydroamination: The aminoalkynes (740 µmol) were dissolved in
C6D6 (0.5 mL) and added to the precatalyst (e.g. 7.40 µmol for
1 mol-%) and then to the cocatalyst [PhNMe2H][SO3CF3]
(7.40 µmol for 1 mol-%). The mixture was injected into an NMR (CHAr), 132.6 (C), 145.9 (C), 162.4 (C), 162.8 (C) ppm. IR (ATR):
tube, removed from the glovebox, cooled to –196 °C, and flame-
sealed under vacuum. The reaction mixture was then heated to
ν = 3156, 3103, 2961, 2933, 2863, 1700, 1596, 1574, 1531, 1452,
˜
1383, 1280, 1041, 800 cm–1. MS (EI, 70 eV, 160 °C): m/z (%) = 367
1076
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1070–1081

β-Diketiminate Zinc Complexes for the Hydroamination of Alkynes
(47) [M+ – HCl], 352 (26), 324 (72), 200 (59), 166 (57), 153 (82),
84 (100). HRMS: calcd. for C24H37N3 367.2988; found 367.2988.
1149, 1101, 1016, 857, 836, 746, 730, 657 cm–1. MS (EI, 70 eV,
170 °C): m/z (%) = 412 (75) [M+], 397 (100) [M+ – Me], 333 (25),
279 (17), 172 (13), 160 (63), 158 (18), 145 (14), 119 (35), 91 (17).
HRMS: calcd. for C24H32N2Zn 412.1857; found 412.1852.
C24H32N2Zn (413.91): calcd. C 69.64, H 7.79, N 6.77; found C
69.58, H 7.97, N 6.65.
[2-(1-Cyclohexyl-imidazolidine-2-ylidene)-1-methylethylidene]-(2,6-
diisopropylphenyl)amine (10): To a solution of 10·HCl (470 mg,
1.16 mmol) in methanol (10 mL) was added Amberlite® IRA-
400(OH) (3 mL), and the suspension was stirred overnight. After
filtration of the mixture, the filtrate was concentrated under re-
duced pressure. The crude product was then dissolved in ether and
filtered over Celite®. After concentration of the filtrate, 10 was ob-
tained as a colorless oil that crystallized to a white solid overnight.
[{N,NЈ-Bis(4-methoxyphenyl)-β-diketiminato}methylzinc] (4): A
solution of ZnMe2 (1.2  in toluene, 4 mL, 4.8 mmol) in toluene
(10 mL) was treated dropwise with a solution of the corresponding
ligand (300 mg, 0.97 mmol) in toluene (10 mL) at –20 °C over 3 h.
The reaction mixture was slowly warmed up to room temperature
and stirred overnight. The yellow solution was concentrated in
vacuo and dried at 60 °C to give 90% of the desired compound 4
and 10 % by-product 5 as a brown solid. 1H NMR (400 MHz,
C6D6): δ = –0.40 (s, 3 H, CH3), 1.91 (s, 6 H, CH3), 3.33 (s, 6 H,
OCH3), 4.97 (s, 1 H, CH), 6.77 (m, 8 H, CHAr) ppm. 13C NMR
(100 MHz, C6D6): δ = –20.8 (CH3), 23.1 (CH3), 54.6 (CH3), 96.9
(CH), 114.1 (CHAr), 125.4 (CHAr), 143.0 (C), 156.7 (C), 166.3 (C)
1
Yield: 346 mg (81%). M.p. 116 °C. H NMR (400 MHz, CDCl3):
δ = 1.13 (d, J = 6.8 Hz, 6 H, CH3), 1.17 (d, J = 7.0 Hz, 6 H, CH3),
1.38 (m, 4 H, CH2), 1.63 (s, 3 H, CH3), 1.70 (m, 2 H, CH2), 1.84
(m, 4 H, CH2), 3.10 (septet, J = 6.9 Hz, 2 H, CH), 3.26 (t, J =
8.8 Hz, 2 H, CH2), 3.55 (m, 1 H, CH), 3.63 (t, J = 8.8 Hz, 2 H,
CH2), 4.42 (s, 1 H, CH), 7.11 (m, 3 H, CHAr) ppm. 13C NMR
(125 MHz, CDCl3): δ = 20.8 (CH3), 22.9 (CH3), 24.5 (CH3), 25.8
(CH2), 25.9 (CH2), 28.1 (CH), 30.3 (CH2), 43.3 (CH2), 48.4 (CH2),
53.7 (CH), 77.2 (CH), 122.9 (CHAr), 125.2 (CHAr), 128.9 (C), 144.3
ppm. IR (ATR): ν = 3633, 3033, 2954, 2832, 1606, 1550, 1500,
˜
1455, 1401, 1271, 1238, 1199, 1179, 1103, 1033, 939, 861, 822,
654 cm–1. MS (EI, 70 eV, 100 °C): m/z (%) = 388 (81) [M+], 373
(100) [M+ – Me], 358 (38), 328 (9), 309 (35), 267 (27), 189 (8), 148
(52), 146 (11), 92 (11), 79 (12), 77 (16), 69 (20), 57 (8). HRMS:
calcd. for C20H24N2O2Zn 388.1129; found 388.1136.
(C), 163.1 (C) ppm. IR (ATR): ν = 3061, 2959, 2931, 2856, 1626,
˜
1528, 1451, 1387, 1312, 1276, 1172, 759 cm–1. MS (EI, 70 eV,
230 °C): m/z (%) = 368 (71) [M+ + H], 353 (49), 324 (100), 242 (28),
202 (68), 200 (71), 153 (80), 84 (97). HRMS: calcd. for C24H38N3
208.1576; found 208.1578. C24H37N3 (367.58): calcd. C 78.42, H
10.15, N 11.43; found C 78.06, H 10.46, N 11.30.
[Bis{N,NЈ-bis(4-methoxyphenyl)-β-diketiminato}zinc] (5): A solution
of the corresponding ligand (300 mg, 0.97 mmol) in toluene (5 mL)
was treated dropwise with ZnMe2 (1.2  in toluene, 0.5 mL,
0.6 mmol) for 0.5 h at room temperature and stirred overnight. The
yellow solution was dried in vacuo at 60 °C to give a quantitative
yield of the desired compound as a yellow powder. M.p. 159 °C.
1H NMR (400 MHz, C6D6): δ = 1.85 (s, 12 H, CH3), 3.36 (s, 12 H,
CH3), 4.69 (s, 2 H, CH), 6.85 (m, 16 H, CHAr) ppm. 13C NMR
(125 MHz, C6D6): δ = 23.0 (CH3), 54.6 (CH3), 95.7 (CH), 113.8
(CHAr), 125.5 (CHAr), 143.8 (C), 156.3 (C), 166.1 (C) ppm. IR
Metal-Complex Synthesis
[{N,NЈ-Bis(2-isopropylphenyl)-β-diketiminato}methylzinc] (2): To a
solution of ZnMe2 (1.2  in toluene, 2.5 mL, 3 mmol) in toluene
(5 mL) was slowly added a solution of the corresponding ligand
(200 mg, 0.6 mmol) in toluene (5 mL) at –20 °C. The reaction mix-
ture was warmed up to room temperature and stirred overnight at
80 °C. The clear solution was concentrated in vacuo and dried at
60 °C to give a quantitative yield of the desired compound as a
yellowish oil, which crystallized in 3 d to a white solid. M.p. 105 °C.
1H NMR [400 MHz, C6D6, mixture of E/E and E/Z isomers (1:1)]:
δ = –0.58 (s, 3 H, CH3), –0.53 (s, 3 H, CH3), 1.13 (d, J = 6.9 Hz,
6 H, CH3), 1.16 (d, J = 6.9 Hz, 6 H, CH3), 1.20 (d, J = 6.9 Hz, 6
H, CH3), 1.25 (d, J = 6.9 Hz, 6 H, CH3), 1.76 (s, 6 H, CH3), 1.78
(s, 6 H, CH3), 3.27 (m, 4 H, CH), 4.96 (s, 1 H, CH), 5.02 (s, 1 H,
CH), 6.83 (m, 4 H, CHAr), 7.05 (m, 8 H, CHAr), 7.22 (m, 4 H,
CHAr) ppm. 13C NMR (100 MHz, C6D6): δ = –17.9 (CH3), –17.9
(CH3), 22.8 (CH3), 23.1 (CH3), 23.2 (CH3), 23.3 (CH3), 23.5 (CH3),
23.6 (CH3), 27.8 (CH), 27.8 (CH), 95.7 (CH), 95.9 (CH), 124.8
(CHAr), 125.0 (CHAr), 125.3 (CHAr), 125.4 (CHAr), 125.9 (CHAr),
126.0 (CHAr), 126.3 (CHAr), 126.3 (CHAr), 141.5 (C), 141.6 (C),
(ATR): ν = 3033, 2950, 2832, 1625, 1606, 1549, 1500, 1453, 1399,
˜
1269, 1238, 1199, 1180, 1104, 1035, 939, 860, 821, 785 cm–1. MS
(EI, 70 eV, 210 °C): m/z (%) = 682 (79) [M+], 667 (6), 561 (22), 373
(21), 341 (9), 309 (32), 189 (45), 148 (83), 92 (100), 69 (28). HRMS:
calcd. for C3 8 H4 2 N4 O4 Zn 682.2498; found 682.2505.
C38H42N4O4Zn (684.15): calcd. C 66.71, H 6.19, N 8.19; found C
66.38, H 6.25, N 8.13.
[{2-(1-Cyclohexyl-imidazolidine-2-ylidene)-1-methylethylidene-(2,6-
diisopropylphenyl)aminato}bis(trimethysilylamido)zinc] (6): A solu-
tion of Zn{N(SiMe3)2}2 (246 mg, 0.64 mmol) in hexane (5 mL) was
treated dropwise with 9 (216 mg, 0.59 mmol) in hexane (5 mL) and
stirred overnight at room temperature. Subsequently, the solution
was concentrated at reduced pressure, and the crude product was
recrystallized at –20 °C. Compound 6 was obtained as white crys-
tals. Yield: 255 mg (73 %). M.p. 164 °C. 1H NMR (400 MHz,
C6D6): δ = 0.29 (s, 18 H, CH3), 0.88 (m, 1 H, CH2), 1.07 (m, 4 H,
CH2), 1.22 (d, J = 6.8 Hz, 6 H, CH3), 1.41 (d, J = 6.9 Hz, 6 H,
CH3), 1.45 (m, 1 H, CH2), 1.60 (m, 4 H, CH2), 1.76 (s, 3 H, CH3),
2.86 (t, J = 9.2 Hz, 2 H, CH2), 3.31 (m, 1 H, CH), 3.42 (septet, J
= 6.8 Hz, 2 H, CH), 3.75 (t, J = 9.2 Hz, 2 H, CH2), 4.60 (s, 1 H,
147.3 (C), 147.4 (C), 166.6 (C), 166.8 (C) ppm. IR (ATR): ν =
˜
3623, 3063, 3019, 2960, 2926, 2867, 1646, 1626, 1596, 1554, 1520,
1480, 1443, 1407, 1365, 1341, 1282, 1209, 1183, 1086, 1032, 941,
838, 753, 658 cm–1. MS (EI, 70 eV, 120 °C): m/z (%) = 412 (57)
[M+], 397 (100) [M+ – Me], 333 (22), 200 (10), 160 (58), 158 (28),
144 (24). HRMS: calcd. for C24H32N2Zn 412.1857; found 412.1855.
C24H32N2Zn (413.91): calcd. C 69.64, H 7.55, N 6.77; found C
69.30, H 7.64, N 6.33.
[{N,NЈ-Bis(2,4,6-trimethylphenyl)-β-diketiminato}methylzinc] (3): CH), 7.20 (m, 3 H, CHAr) ppm. 13C NMR (125 MHz, C6D6): δ =
The synthesis was similar to that of 2. Compound 3 was isolated 5.4 (CH3), 24.5 (CH3), 24.8 (CH3), 24.9 (CH3), 25.7 (CH2), 25.9
in quantitative yield as a white powder. M.p. 117 °C. 1H NMR (CH2), 28.2 (CH), 30.3 (CH2), 43.2 (CH2), 48.9 (CH2), 53.7 (CH),
(400 MHz, C6D6): δ = –0.56 (s, 3 H, CH3), 1.68 (s, 6 H, CH3), 2.17 77.0 (CH), 124.0 (CHAr), 125.8 (CHAr), 143.1 (C), 145.5 (C), 165.2
(s, 12 H, CH3), 2.19 (s, 6 H, CH3), 5.03 (s, 1 H, CH), 6.86 (s, 4 H, (C), 166.8 (C) ppm. MS (EI, 70 eV, 90 °C): m/z (%) = 590 (5) [M+],
CHAr) ppm. 13C NMR (100 MHz, C6D6): δ = –18.7 (CH3), 18.4
(CH3), 20.6 (CH3), 22.3 (CH3), 95.4 (CH), 129.2 (CHAr), 130.5 (C),
575 (10), 429 (50), 202 (14), 146 (100), 130 (56), 73 (9). HRMS:
calcd. for C3 0 H5 3 N4 Si2 Zn 589.3100; found 589.3090.
133.4 (C), 145.2 (C), 166.8 (C) ppm. IR (ATR): ν = 3687, 2999, C30H54N4Si2Zn (592.34): calcd. C 60.83, H 9.19, N 9.46; found C
˜
2911, 2852, 1663, 1546, 1524, 1456, 1401, 1375, 1261, 1233, 1205,
60.16, H 9.65, N 9.25.
Eur. J. Inorg. Chem. 2010, 1070–1081
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1077

P. W. Roesky, S. Blechert et al.
FULL PAPER
[{N,NЈ-Bis(2,6-diisopropylphenyl)-β-diketiminato}(trifluoromethane- pressure and
purification by bulb-to-bulb distillation
sulfonato)zinc]·thf (7): To a solution of 1 (200 mg, 0.40 mmol) in
thf (3 mL) was added the cocatalyst [PhNMe2H][SO3CF3] (109 mg,
0.40 mmol). The reaction mixture was stirred overnight at 60 °C in
a sealed tube. The clear solution was heated for 2 h at 120 °C and
recrystallized at room temperature to give 7 as white crystals. Yield:
132 mg (47%). 1H NMR (400 MHz, C6D6): δ = 1.20 (d, J = 6.8 Hz,
(4.0ϫ10–2 mbar, 150 °C), 11c was obtained as a yellowish oil.
1
Yield: 2.7 g (81%). H NMR (400 MHz, CDCl3): δ = 1.71 (s, 1 H,
NH), 2.42 (t, J = 2.3 Hz, 1 H, CH), 2.84 (t, J = 5.1 Hz, 2 H, CH2),
3.66 (t, J = 5.1 Hz, 2 H, CH2), 3.82 (s, 2 H, CH2), 4.15 (d, J =
2.3 Hz, 2 H, CH2), 7.29 (m, 5 H, CHAr) ppm. 13C NMR (100 MHz,
CDCl3): δ = 48.6 (CH2), 53.8 (CH2), 58.3 (CH2), 69.4 (CH2), 74.4
12 H, CH3), 1.26 (m, 4 H, CH2), 1.39 (d, J = 6.6 Hz, 12 H, CH3), (CH), 79.7 (C), 126.9 (CHAr), 128.2 (CHAr), 128.4 (CHAr), 140.2
1.63 (s, 6 H, CH3), 3.29 (m, 4 H, CH), 3.55 (m, 4 H, CH2), 4.77 (s,
(C) ppm. IR (ATR): ν = 3294, 3027, 2920, 2853, 1453, 1353, 1099,
˜
1 H, CH), 7.18 (m, 6 H, CHAr) ppm. 13C NMR (100 MHz, C6D6):
737, 699 cm–1. MS (EI, 70 eV, room temperature): m/z (%) = 189
δ = 23.9 (CH3), 24.4 (CH3), 24.5 (CH3), 25.2 (CH2), 28.3 (CH), (64) [M+], 160 (4), 120 (5), 98 (20), 92 (9), 91 (100), 65 (11). HRMS:
70.6 (CH2), 95.3 (CH), 124.3 (CHAr), 126.7 (CHAr), 142.9 (C),
calcd. for C12H15NO 189.1154; found 189.1151.
143.4 (C), 170.6 (C) ppm. 19F NMR (470.6 MHz, CDCl3): δ =
Phenyl(2-prop-2-ynyloxyethyl)amine (11e): To a solution of N-phen-
ylaminoethanol (6.0 g, 43.7 mmol) in thf (100 mL) was added NaH
(75% in mineral oil, 2.1 g, 65.6 mmol) at –20 °C. After 0.5 h, 3-
bromopropyne (80% in toluene, 5.1 mL, 45.7 mmol) was added,
and the reaction mixture was stirred overnight at room tempera-
ture. After aqueous workup and extraction with diethyl ether
(3ϫ150 mL), the crude product was dried with MgSO4 and con-
centrated under reduced pressure. The residue was purified by bulb-
to-bulb distillation (2.9 mbar, 175 °C) to afford 11f as a yellowish
–77.42 ppm. IR (ATR): ν = 3473, 3222, 3055, 2964, 2931, 2870,
˜
1700, 1549, 1462, 1277, 1240, 1165, 1030, 800, 758 cm–1.
Catalysis
N,NЈ-Dimethylphenylammonium Trifluoromethanesulfonate [PhN-
Me2H][SO3CF3]: To
a solution of N,NЈ-dimethylphenylamine
(1.5 g, 12.5 mmol) in hexane (20 mL) was added trifluoromethane
sulfonic acid (1.9 g, 12.5 mmol); the mixture was stirred for 1 h at
room temperature. Subsequently, the solution was concentrated at
reduced pressure and [PhNMe2H][SO3CF3] was obtained quantita-
tively as a colorless oil that crystallized to colorless crystals upon
standing. M.p. 38 °C. 1H NMR (400 MHz, CDCl3): δ = 3.31 (d, J =
5.0 Hz, 6 H, CH3), 7.54 (m, 5 H, CHAr) ppm. 13C NMR (100 MHz,
CDCl3): δ = 47.4 (CH3), 120.2 (CHAr), 120.4 (CF3), 130.8 (CHAr),
130.9 (CHAr), 142.1 (C) ppm. 19F NMR (470.6 MHz, CDCl3): δ =
1
oil. Yield: 6.9 g (90%). H NMR (400 MHz, CDCl3): δ = 2.51 (dt,
J = 0.6, J = 2.4 Hz, 1 H, CH), 3.36 (dt, J = 2.8, J = 5.4 Hz, 2 H,
CH2), 3.78 (dt, J = 2.8, J = 5.6 Hz, 2 H, CH2), 3.97 (br. s, 1 H,
NH), 4.22 (dt, J = 0.6, J = 2.4 Hz, 2 H, CH2), 6.68 (m, 2 H, CHAr),
6.77 (m, 1 H, CHAr), 7.23 (m, 2 H, CHAr) ppm. 13C NMR
(125 MHz, CDCl3): δ = 43.5 (CH2), 58.3 (CH2), 68.5 (CH2), 74.9
(CH), 79.7 (C), 113.2 (CHAr), 117.7 (CHAr), 126.3 (CHAr), 148.2
–78.09 ppm. IR (ATR): ν = 3472, 3052, 2771, 1497, 1282, 1239,
˜
(C) ppm. IR (ATR): ν = 3400, 3285, 2924, 2855, 1602, 1505, 1318,
1160, 1027, 900, 767, 693 cm–1. MS (EI, 70 eV, 80 °C): m/z (%) =
121 (75), 120 (100), 105 (13), 77 (22), 51 (9). C19H12F3NO3S
(391.36): calcd. C 39.85, H 4.46, N 5.16; found C 39.51, H 4.47, N
5.21.
˜
1264, 1095, 749, 693 cm–1. MS (EI, 70 eV, room temperature): m/z
(%) = 175 (18) [M+], 106 (100), 77 (12). HRMS: calcd. for
C11H13NO 175.0997; found 175.0996.
Hex-5-ynylpyrimidin-2-ylamine (11f): Hex-5-ynylamine (806 mg,
8.30 mmol), 2-chloropyrimidine (1.2 g, 10.5 mmol), and K2CO3
(1.0 g, 7.2 mmol) were stirred in dmf (20 mL) for 2 d at 70 °C. After
aqueous workup and extraction with dichloromethane
(2ϫ100 mL), the crude product was dried with MgSO4 and con-
centrated under reduced pressure. The residue was purified by flash
column chromatography (SiO2, cyclohexane/EtOAc, 3:1) to afford
N-Benzyl-(2-prop-2-ynyloxyethyl)amine (11a): 2-(Benzylidene-
amino)ethanol (3.0 g, 20.1 mmol) in thf (20 mL) was added to a
suspension of NaH (60% in mineral oil, 1.2 g, 30.0 mmol) and 3-
bromopropyne (80% in toluene, 3.4 mL, 30.2 mmol) in thf (30 mL).
The reaction mixture was heated for 3 h at 60 °C and then left at
room temperature overnight. After the aqueous workup and extrac-
tion with diethyl ether (2ϫ30 mL), the organic phase was first
washed with water (40 mL) and then with a concentrated NaCl
solution (40 mL). Subsequently, the crude product was dried with
MgSO4 and concentrated under reduced pressure. The residue was
purified by bulb-to-bulb distillation (4.0ϫ10–2 mbar, 125 °C) to af-
ford N-benzylidene(2-prop-2-ynyloxyethyl)amine as a yellowish oil.
1
11e as a white solid. Yield: 963 mg (66%). M.p. 59 °C. H NMR
(400 MHz, CDCl3): δ = 1.62 (m, 2 H, CH2), 1.74 (m, 2 H, CH2),
1.95 (t, J = 2.6 Hz, 1 H, CH), 2.24 (dt, J = 2.6, J = 6.9 Hz, 2 H,
CH2), 3.43 (dt, J = 5.9, J = 7.0 Hz, 2 H, CH2), 5.24 (br. s, 1 H,
NH), 6.50 (t, J = 4.8 Hz, 1 H, CHAr), 8.26 (d, J = 4.8 Hz, 2 H,
CHAr) ppm. 13C NMR (125 MHz, CDCl3): δ = 18.2 (CH2), 25.8
(CH2), 28.7 (CH2), 40.9 (CH2), 68.6 (CH), 84.1 (C), 110.4 (CHAr),
1
Yield: 3.5 g (93%). H NMR (400 MHz, CDCl3): δ = 2.42 (t, J =
2.3 Hz, 1 H, CH), 3.84 (m, 4 H, CH2), 4.19 (d, J = 2.3 Hz, 2 H,
CH2), 7.41 (m, 3 H, CHAr), 7.74 (m, 2 H, CHAr), 8.32 (s, 1 H, CH)
ppm. 13C NMR (100 MHz, CDCl3): δ = 46.7 (CH2), 62.5 (CH2),
63.2 (CH2), 77.2 (CH), 92.6 (C), 128.2 (CHAr), 128.6 (CHAr), 130.9
158.0 (CHAr), 162.4 (C) ppm. IR (ATR): ν = 3231, 2943, 2868,
˜
1593, 1535, 1451, 1379, 1120, 801, 686 cm–1. MS (EI, 70 eV, room
temperature): m/z (%) = 174 (11) [M+ – H], 146 (20), 136 (9), 108
(100), 95 (11), 79 (14). HRMS: calcd. for C10H12N3 174.1031;
found 174.1031.
(CHAr), 135.9 (C), 163.1 (CH) ppm. IR (ATR): ν = 3293, 3061,
˜
3027, 2850, 1647, 1451, 1100, 1032, 918, 755, 693 cm–1. MS (EI,
70 eV, room temperature): m/z (%) = 186 (29) [M+ – H], 156 (3),
133 (28), 118 (76), 104 (21), 91 (100), 77 (9), 65 (8), 51 (9). HRMS:
calcd. for C12H12NO 186.0919; found 186.0915.
Hex-5-ynyl-(4-nitro-phenyl)-amine (11g): Hex-5-ynylamine (629 mg,
6.47 mmol), 1-fluoro-4-nitrobenzene (1.1 g, 7.8 mmol), and K2CO3
(630 mg, 4.56 mmol) were stirred in dmf (10 mL) overnight. After
aqueous workup and extraction with diethyl ether (2ϫ100 mL),
the crude product was dried with MgSO4 and concentrated under
reduced pressure. The residue was purified by flash column
chromatography (SiO2, cyclohexane/ether, 3:1) to afford 11g as yel-
The isolated imine intermediate (3.3 g, 17.6 mmol) was then dis-
solved in methanol (50 mL) and NaBH4 (2.7 g, 71.3 mmol) was
added at 0 °C. After 1 h at 0 °C, the reaction mixture was stirred
overnight at room temperature and then concentrated at reduced
pressure. After aqueous workup and extraction with diethyl ether
(3ϫ30 mL), the organic phase was washed with water (40 mL),
then with a concentrated NaCl solution (40 mL), and dried with
MgSO4. After concentration of the crude product under reduced
1
low crystals. Yield: 1.0 g (72%). M.p. 60 °C. H NMR (400 MHz,
CDCl3): δ = 1.65 (m, 2 H, CH2), 1.81 (m, 2 H, CH2), 1.99 (t, J =
2.6 Hz, 1 H, CH), 2.27 (dt, J = 2.6, J = 6.9 Hz, 2 H, CH2), 3.25
(t, J = 7.1 Hz, 2 H, CH2), 4.64 (br. s, 1 H, NH), 6.53 (m, 2 H,
1078
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1070–1081

β-Diketiminate Zinc Complexes for the Hydroamination of Alkynes
CHAr), 8.09 (m, 2 H, CHAr) ppm. 13C NMR (125 MHz, CDCl3): J = 4.8 Hz, 1 H, CHAr), 8.26 (d, J = 4.8 Hz, 2 H, CHAr) ppm. 13C
δ = 18.1 (CH2), 25.7 (CH2), 28.0 (CH2), 43.0 (CH2), 69.1 (CH), NMR (125 MHz, CDCl3): δ = 21.0 (CH2), 29.1 (CH2), 30.0 (CH3),
83.7 (C), 111.2 (CHAr), 126.5 (CHAr), 138.1 (C), 153.1 (C) ppm.
41.1 (CH2), 43.2 (CH2), 110.4 (CHAr), 158.0 (CHAr), 162.3 (C),
IR (ATR): ν = 3376, 3292, 2941, 2864, 1600, 1470, 1302, 1184,
208.7 (C) ppm. IR (ATR): ν = 3273, 2936, 2864, 1712, 1587, 1533,
˜
˜
1111, 832, 753 cm–1. MS (EI, 70 eV, room temperature): m/z (%) =
218 (16) [M+], 166 (10), 151 (100), 105 (35), 84 (19). HRMS: calcd.
for C12H14N2O2 218.1055; found 218.1042.
1454, 1365, 1164, 802 cm–1. MS (EI, 70 eV, room temperature): m/z
(%) = 193 (20) [M+], 150 (15), 122 (22), 108 (100), 95 (12), 79 (7).
HRMS: calcd. for C10H13N3O 193.1215; found 193.1213.
4-Benzyl-5-methyl-3,4-dihydro-2H-[1,4]oxazine (12a): Compound
12a was prepared according to the method described in the General
Methods and Instruments Section and was characterized after con-
centration of the reaction mixture under reduced pressure. 1H
NMR (400 MHz, C6D6): δ = 1.62 (d, J = 1.1 Hz, 3 H, CH3), 2.72
(t, J = 4.2 Hz, 2 H, CH2), 3.62 (t, J = 4.2 Hz, 2 H, CH2), 3.70 (s,
3 H, CH2), 5.99 (q, J = 1.2 Hz, 1 H, CH), 7.15 (m, 1 H, CHAr),
7.22 (m, 4 H, CHAr) ppm. 13C NMR (100 MHz, C6D6): δ = 15.9
(CH3), 47.4 (CH2), 55.0 (CH2), 62.2 (CH2), 121.4 (C), 125.3 (CH),
127.2 (CHAr), 128.4 (CHAr), 128.6 (CHAr), 139.5 (C) ppm. IR
6-(4-Nitrophenylamino)-hexan-2-one (12g): Compound 12g was pre-
pared according to the method described in the General Methods
and Instruments Section and was purified by flash column
chromatography (SiO2, cyclohexane/EtOAc, 3:1) to afford yellow
crystals. Yield: (Table 1). M.p. 87 °C. 1H NMR (400 MHz, CDCl3):
δ = 1.67 (m, 4 H, CH2), 2.16 (s, 3 H, CH3), 2.52 (t, J = 6.6 Hz, 2
H, CH2), 3.21 (t, J = 6.6 Hz, 2 H, CH2), 4.69 (br. s, 1 H, NH), 6.2
(m, 2 H, CHAr), 8.08 (m, 2 H, CHAr) ppm. 13C NMR (125 MHz,
CDCl3): δ = 20.7 (CH2), 28.4 (CH2), 30.1 (CH3), 42.9 (CH2), 43.1
(CH2), 110.9 (CHAr), 126.5 (CHAr), 137.9 (C), 153.3 (C), 208.5 (C)
(ATR): ν = 3381, 3085, 3062, 3027, 2957, 2926, 2853, 1713, 1652,
˜
ppm. IR (ATR): ν = 3380, 3362, 2945, 1711, 1600, 1465, 1299,
˜
1277, 1109, 832, 754 cm–1. MS (EI, 70 eV, 80 °C): m/z (%) = 236
(21) [M+], 202 (17), 151 (100), 105 (25), 84 (41). HRMS: calcd.
for C12H16N2O3 236.1161; found 236.1153. C12H16N2O3 (236.27):
calcd. C 61.00, H 6.83, N 11.86; found C 61.08, H 6.74, N 11.74.
1604, 1585, 1540, 1495, 1452, 1361, 1317, 1252, 1202, 1160, 1126,
1090, 1070, 1028, 999, 973, 895, 822, 731, 698 cm–1. MS (EI, 70 eV,
100 °C): m/z (%) = 189 (42) [M+], 98 (14), 92 (7), 91 (100), 70 (7),
65 (16), 63 (4), 56 (3), 51 (5). HRMS: calcd. for C12H15NO
189.1154; found 189.1154.
X-ray Crystallographic Studies of 2–7: Crystals of 2 were obtained
from hexane. Crystals of 3–6 were grown from toluene/pentane or
toluene/hexane. A suitable crystal was covered in mineral oil (Ald-
rich) and mounted onto a glass fiber. The crystal was transferred
directly to the –73 °C cold stream of a Stoe IPDS II. Crystals of 3
were measured at room temperature on a Bruker Smart 1000 CCD
diffractometer. Subsequent computations were carried out on an
Intel Pentium IV PC. All structures were solved by the direct meth-
ods (SHELXS-97[44]). The remaining non-hydrogen atoms were lo-
cated from successive difference Fourier map calculations. The re-
finements were carried out by using full-matrix least-squares tech-
niques on F with the program SHELXL-97, by minimizing the
function (Fo – Fc)2, where the weight is defined as 4Fo2/2(Fo2) and
Fo and Fc are the observed and calculated structure factor ampli-
tudes.[44] Carbon-bound hydrogen atom positions were calculated
5-Methyl-4-phenyl-3,4-dihydro-2H-[1,4]oxazine (12e): Compound
12e was prepared according to the method described in the General
Methods and Instruments Section and was characterized according
to the literature[15] by NMR spectroscopy. 1H NMR (400 MHz,
C6D6): δ = 1.61 (t, J = 1.0 Hz, 3 H, CH3), 3.19 (dt, J = 0.8, J =
4.1 Hz, 2 H, CH2), 3.59 (dt, J = 0.8, J = 4.1 Hz, 2 H, CH2), 6.17
(t, J = 1.0 Hz, 1 H, CH), 6.91 (m, 3 H, 1-H, CHAr), 7.17 (m, 2 H,
CHAr) ppm. 13C NMR (125 MHz, C6D6): δ = 15.9 (CH3), 51.5
(CH2), 62.0 (CH2), 116.8 (C), 122.3 (CHAr), 123.4 (CHAr), 129.2
(CHAr), 130.4 (CH), 148.7 (C) ppm.
6-(Pyrimidin-2-ylamino)hexan-2-one (12f): Compound 12f was pre-
pared according to the method described in the General Methods
and Instruments Section and was purified by flash column
chromatography (SiO2, EtOAc/cyclohexane) to afford a colorless
1
oil. Yield: (Table 1). H NMR (400 MHz, CDCl3): δ = 1.64 (m, 4 and allowed to ride on the carbon atom to which they are bonded.
H, CH2), 2.13 (s, 3 H, CH3), 2.48 (t, J = 7.0 Hz, 2 H, CH2), 3.41
The hydrogen atom contributions were calculated, but not refined.
(q, J = 6.5 Hz, 2 H, CH2), 5.24 (br. s, 1 H, NH), 6.51 (dt, J = 0.7, The final values of refinement parameters are given in Table 3. The
Table 3. Crystallographic details of 3–7.[a]
3
4
5
6
7
Formula
Formula weight
Space group
a [Å]
b [Å]
c [Å]
C24H32N2Zn
413.9
C20H24N2O2Zn
389.78
C38H42N4O4Zn
684.13
C30H54N4Si2Zn
592.32
C34H49F3N2O4SZn
704.18
P21/n (No. 14)
8.8435(2)
32.1619(9)
16.7764(4)
104.9290(10)
4610.5(2)
8
P21/n (No. 14)
14.4626(12)
8.1213(4)
17.7717(13)
113.536(6)
1913.7(2)
4
P21/c (No. 14)
20.813(4)
9.018(2)
18.049(4)
90.21(3)
3387.4(12)
4
P21/n (No. 14)
11.3829(8)
10.3885(6)
28.832(2)
101.408(5)
3342.0(4)
4
P21/c (No. 14)
12.329(3)
13.596(3)
21.531(4)
90.35(3)
3609.0(13)
4
1.296
β [°]
V [Å3]
Z
Density [gcm–3]
Radiation
µ [mm–1]
1.193
1.353
1.341
1.177
MoKα (λ = 0.71073 Å) MoKα (λ = 0.71073 Å) MoKα (λ = 0.71073 Å) MoKα (λ = 0.71073 Å) MoKα (λ = 0.71073 Å)
1.075
1.298
0.771
0.830
0.791
Absorption correction none
Integration (X-Shape)
13200
5101 [Rint = 0.0256]
4277
5101/229
0.0354; 0.0996
Integration (X-Shape)
18953
8907 [Rint = 0.0646]
5781
8907/432
0.0442; 0.1082
Integration (X-Shape)
17286
8587 [Rint = 0.0634]
5513
8587/345
0.0443; 0.0843
none
25135
6866 [Rint = 0.0488]
6054
6866/413
0.0488; 0.1298
Reflections collected
Unique reflections
Observed reflections
Data/parameters
21524
5808 [Rint = 0.1133]
4338
5808/505
[c]
R1[b]; wR2
0.0464; 0.0977
[a] All data collected at 203 K. [b] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [c] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
2
2 2
Eur. J. Inorg. Chem. 2010, 1070–1081
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1079

P. W. Roesky, S. Blechert et al.
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Received: October 12, 2009
Published Online: January 25, 2010
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